The emergence of correlated, low-frequency (< 30 Hz), rhythmic activity of neurons in the subthalamic nucleus (STN) is critical for the symptomatic expression of Parkinson's disease (PD). GABAergic synaptic inputs from the external globus pallidus and glutamatergic synaptic inputs from the cortex and thalamus are critical for the normal and pathological patterning of STN activity. The principal hypothesis that will be tested by this research is that the loss of dopamine in PD leads to abnormal synaptic transmission within the STN, which (in part) underlies the pathological firing pattern. This hypothesis will be tested using electrophysiological recording of STN neurons in brain slices, correlated light and electron microscopy and 2-photon imaging. The influence of dopamine will be assessed by comparison of synaptic transmission and integration in i) the presence and absence of dopamine receptor agonists/antagonists and 2) in normal and dopamine-depleted animals. There are three specific aims of the project. Specific Aim 1: Measure the short-term plasticity and impact of GABAergic and glutamatergic synaptic transmission and their modulation by dopamine receptor agonists and antagonists. Specific Aim 2: Determine the pre- and/or postsynaptic activity patterns that underlie long-term plasticity of GABAergic and glutamatergic synaptic transmission in the STN. Specific Aim 3: Compare the operation and influence of GABAergic and glutamatergic synapses in the STN in control animals and experimental models of PD. The knowledge generated by this project will further our understanding of the factors underlying pathological activity in the STN and assist the rational development of therapies that ameliorate the symptoms and interrupt the progression of PD by modification of STN activity. Lay Description: Abolition of pathological activity of nerve cells in the subthalamic nucleus (STN) leads to a profound improvement in the symptoms of Parkinson's disease (PD). This project will test the hypothesis that pathological STN activity is driven (in part) by abnormal inputs to STN nerve cells in PD. By elucidating the mechanisms underlying abnormal activity, this research will guide the rational development of therapies that ameliorate the symptoms and interrupt the progression of PD through the normalization of STN activity. [unreadable] [unreadable] [unreadable]